High-profile recruit Benji Marshall will make his Super Rugby debut off the bench when the Blues face the Highlanders in their season opener in Dunedin on Saturday.
The former Wests Tigers playmaker has made an impressive transition to the 15-man code since joining the franchise in December, however Kirwan said he was not quite ready to start and would instead make his impact felt off the pine.
"For the first team we've named the main feature will always be Benji. He's probably the highest profile signing in the off-season and we just feel that he's not quite ready from a learning and understanding of the game," said Kirwan.
"He's the first one to admit he's not quite ready so that was probably the biggest selection situation we had."
Marshall will cover the five-eighths and full-back positions, with Kirwan having full faith in him to perform when required.
"We wouldn't put him on the bench if we didn't think he could cover both roles pretty competently so we've got him there to cover that. You know what it's like with the modern game, he'll be getting some game time."
After having neck surgery in the off-season, Chris Noakes has recovered well and will direct the team at first five-eighths.
"He was one of our stars last year at the beginning of the season and I think he's done that again for us in the last week or so. He's just stepped into that role, he's working really hard around his contact and is driving the football team around well," added Kirwan.
"I think it's been a blessing to have Benji there trying to fit into 10. We've had Baden with a broken arm so we've had a few issues there and Noakesy's worked his way into some good form and gets the starting nod."
Another key selection is at loosehead prop where Ofa Tu'ungafasi will make his first start for the Blues after impressing the coaching staff during the pre-season.
"Ofa Tu'ungafasi has had an incredible pre-season and just really deserves his spot. What you've seen from Ofa in the pre-season is heaps of energy, excitement and him throwing himself into everything," revealed Kirwan.
"I think the biggest thing for Ofa is the invisible stuff that people don't see. He's really taken control of his diet, he's lost 10 kilos, he's much more settled as a person, he's really matured and understands what he wants and that's reflected in the way he's trained. He's reaching PBs and also the way he's playing, he just needs to get out there this weekend and keep that energy up."
Veteran Tom Donnelly will play his first game for the Blues against one of his former teams, and he is joined in the locking department by Liaki Moli who has risen to the challenge in the absence of the injured Culum Retallick.
"Liaki's had another good pre-season. He's been really fit, he got a little bit of an injury which put him out of the second game but Liaki is a player that we're expecting to play really well this season," stated Kirwan.
"He's been around a little while now and he's the type of guy we need - he's hard, raw boned, loves the contact area and he's really turned up in shape and ready to go and I'm excited to see him get out there."
Despite producing a number of fine performances at centre during the pre-season, George Moala reverts to the wing for Saturday's clash as Kirwan has gone for the experienced combination of Francis Saili and Jackson Willison in the midfield.
On the bench, Patrick Tuipulotu and Tevita Li join Benji Marshall as the other players who could make their Super Rugby debuts.
Kirwan said the Highlanders posed a huge challenge at Forsyth Barr Stadium.
"The Highlanders are the favourites, we're down at their home, they've got a lot to play for, they've gone under the radar and they'll be trying to hoe into us so it's a big week," acknowledged Kirwan.
"If you want to go down there and underestimate them, what happened last year will happen again so we need to make sure we match them right across the park, and at this time of the season it's going to do down to the wire so we need to be ready for that as well."
Blues: 15 Charles Piutau, 14 Frank Halai, 13 Jackson Willison, 12 Francis Saili, 11 George Moala, 10 Chris Noakes, 9 Piri Weepu, 8 Peter Saili, 7 Luke Braid, 6 Steven Luatua, 5 Tom Donnelly, 4 Liaki Moli, 3 Charlie Faumuina, 2 James Parsons, 1 Ofa Tu'ungafasi
Replacements: 16 Tom McCartney, 17 Sam Prattley, 18 Angus Ta'avao, 19 Patrick Tuipulotu, 20 Brendon O'Connor, 21 Bryn Hall, 22 Benji Marshall, 23 Tevita Li
Date: Saturday, February 22
Venue: Forsyth Barr Stadium, Dunedin
Kickoff: 19:35 (local, 04:35 GMT)
Referee: Chris Pollock (New Zealand)
Assistant Referees: Nick Briant (New Zealand), Mike Lash (New Zealand)
TMO: Chris Watt (New Zealand)